This invention relates to a method of manufacturing denatured polyphenylene ether, and more particularly to such a method involving a gas phase graft polymerization of polyphenylene ether.
Polyphenylene ether has a comparatively high softening point and belongs to a class of thermoplastic resins which are effectively used in fields requiring thermal resistance. However, polyphenylene ether is insufficient in its impact resistance and workability to be utilizable for certain uses.
A variety of methods have been proposed to improve the above mentioned disadvantages. For example, as to impact resistance, a method of denaturing polyphenylene ether by use of a rubber, has been proposed. For example, a method proposed in Japan Patent Publication Nos. 1482/1968 and 32730/1972, mechanically add rubber into polyphenylene ether in their molten state. In another method disclosed in Japan Patent Publication No. 47389/1978, polyphenylene ether and polybutadiene were first dissolved in a conventional solvent, in which they were both soluble. Then, the resulting solution was added a little at a time into another conventional solvent, in which both were substantially insoluble, thereby causing the two components to precipitate out as homogeneously mixed micro particles. However, disadvantageously, these prior methods only employe blending processes. Considered from an industrial viewpoint, and from the viewpoint of compatibility of rubber to polyphenylene ether, it cannot be said that the properties of rubber are sufficiently utilized.
In order to improve this deficiency, Japan Patent Laid-Open Document No. 9098/1977, employes a method wherein rubber-denatured polyphenylene ether, in which rubber is chemically combined to polyphenylene ether, may be obtained by polymerizing phenol according to an oxidizing coupling reaction in the presence of a reaction product between phenol and rubber. Denatured polyphenylene ether obtained according to this method shows an improvement in its elongation, impact resistance and fatigue resistance. However, disadvantageously, this prior method is complicated in the reaction process and the refining process because it requires reaction between rubber and phenol on a Friedel-Crafts catalyzer.
On the other hand, a method wherein resin having excellent fluidity, is blended or a method wherein low molecular additives are added, may be used as a rule, to improve the workability. However, disadvantageously, in some cases, the latter method leads to leakage of the additives from the resin to stain the surface of the molded products. Also, disadvantageously, the method sometimes lowers the mechanical properties of the resin. An example of this method is Japan Patent Publication No. 17812/1968 which discloses a method wherein polystyrene having excellent compatibility with polyphenylene ether is used to improve workability by blending a resin having an excellent fluidity. Also, Japan Patent Laid-Open Document No. 126800/1975 discloses a method wherein styrene monomer containing compounds which are polymerizable according to a free radical mechanism, are grafted onto polyphenylene ether.
In general, copolymers obtained by merely blending different kinds of resins are remarkably different from polymers obtained by grafting, especially in mechanical properties. The latter is superior to the former. The method disclosed in Japan Patent Laid Open Document No. 126800/1975 employes compounds, which are polymerizable in accordance with a free radical mechanism, at a temperature within the range of from 100.degree. to 200.degree. C., and which are graft polymerized to a polyphenylene ether in the presence of a radical initiator, to obtain a graft copolymer which contains no polyphenylene ether homopolymer (according to the Document). The copolymer obtained according to the method, has in a practical manner, improved certain properties, such as workability or thermal resistance. However, disadvantageously, this method readily causes adverse by-reactions because polymerization is performed at a comparatively high temperature of 100.degree. C. or higher. Most of the compounds which are polymerizable in accordance with the free radical mechanism, can be polymerized at a comparatively high temperature. Also, it difficult to obtain graft copolymers having a large polymerization degree of grafting branches. Moreover, sufficient chain transfer onto polyphenylene ether is difficult to obtain at a polymerization temperature of 100.degree. C. or less; that is to say, grafting efficiency is lowered. Thus, it is desired to develope a grafting method which shows a high grafting efficiency, and at comparatively low temperatures.
Japan Patent Publication No. 41383/1971 discloses a method wherein polyphenylene ether is denatured by graft copolymerizing certain compounds to polyphenylene ether. According to this method, polyphenylene ether is replaced by alkali metals and then grafted by an anion polymerization. This prior method is not an industrially useful method of manufacture because it includes ion polymerization and the graft polymerization is adverseley influenced by water, oxygen and impurities contained in the polymerization system.